Light emitting diodes, LEDs, are employed in a wide range of lighting applications. LED light sources are, for example, used to produce white light, and different light qualities are required for different applications. For some applications there is a desire to provide white light having a colour temperature of e.g. approximately 2700K, i.e. a warm white light, while for other applications there is a desire to provide white light having a colour temperature of e.g. approximately 6000K, i.e. a cool white light.
In order to provide white light, one approach is to coat blue LED(s) with a phosphor. A fraction of the blue light from the blue LED is thereby being transformed by the phosphor from shorter wavelengths to longer wavelengths, thereby producing so-called phosphor based white LEDs. The characteristics of the white light, e.g. the colour temperature, can be changed or varied by providing different phosphor materials. The white light characteristics may also be varied by providing different thickness and/or coating of the phosphor. Furthermore, in order to provide a white light having a desirable colour temperature, LEDs providing white light of different temperature are often used and mixed with each other. For example, an LED providing a cool white light may be combined and mixed with an LED providing a warmer white light.
Due to the various applications requiring different kind of white light characteristics and inherent variation of performance in relation to manufacturing of semiconductor products, such as LEDs, quite a number of combinations are possible if e.g. a tunable white colour temperature is required. Therefore, a problem with the above mentioned approach of combining LEDs having different white light is that many light modules have to be available for achieving a desired combination.